1. Technical Field
The present invention relates to a retractor for a seat belt system. More particularly, the present invention relates to a retractor for a seat belt mounted in a vehicle providing a restricting device which can be positively operated.
2. Background Art
A retractor is disclosed in Japanese Patent Unexamined Publication No. JP-A-2000-038110 and Japanese Patent Unexamined Publication No. JP-A-2001-334913.
An electric retractor described in the above-referenced Japanese Patent Documents includes: a frame; a reel shaft pivotally attached to the frame which winds a seat belt; and a lock mechanism for locking the seat belt so that it can not be drawn out when a predetermined deceleration acts on a vehicle or when the seat belt is drawn out at a predetermined acceleration. A central axis of the reel shaft is connected to a central axis of a pulley for the reel shaft, and the pulley for the reel shaft is connected to a pulley for DC motor via a power transmission belt. A central axis of the pulley for DC motor is connected to DC motor. Accordingly, power of the DC motor is transmitted to the reel shaft. Rotation of the reel shaft, which rotates when a user draws out the seat belt, is also transmitted to DC motor.
Further, various control is performed on the DC motor by MPU (Micro Processing Unit) via DC motor drive system. MPU is connected to a vehicle speed detecting system for detecting a running speed of the vehicle. MPU is also connected to a collision prediction detecting system for detecting whether or not there is a possibility of collision. MPU is also connected to a buckle connecting detection system for detecting whether or not the user fastens the seat belt. According to the result of the detection, the DC motor is driven.
However, in the above conventional design, electric power is required to wind the webbing by the DC motor. Therefore, in the case of the occurrence of trouble in which the motor can not be driven for some reasons or the electric power supply is stopped, it becomes impossible to wind the webbing. Accordingly, in the case of the above malfunction, there is a possibility that the user is not restricted by the seat belt in a desired condition.
The present invention addresses the above shortcomings of the prior art. It is an object of the present invention to provide a retractor for a seat belt capable of positively restricting a user of the seat belt so even at the time of the occurrence of malfunction in which the motor is not operated or the supply of electric power is stopped.